Dismiss Notice

Welcome To CK5!

Registering is free and easy! Hope to see you on the forums soon.

Score a FREE t-shirt and membership sticker when you sign up for a Premium Membership and choose the recurring plan.

Clunking

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by ftn96, Sep 26, 2000.

  1. ftn96

    ftn96 1/2 ton status

    Joined:
    Sep 26, 2000
    Posts:
    3,238
    Likes Received:
    0
    Location:
    Nashville Tn
    Got a solid clunck when putting "Bertha" in drive and in reverse. U-joints and motor/tranny mounts are good. Also get a clunk in the rear as I come to a stop and again as I take off. Brake drums, or rear end on its way??? 10 bolt 8.5 (stock) 150,000 miles.
     
  2. Blazer1970

    Blazer1970 1/2 ton status

    Joined:
    Feb 17, 2000
    Posts:
    1,600
    Likes Received:
    0
    Location:
    Old Mission, MI
    It is pretty much normal for NP241 slip yoke outputs to make a clunk on take-off, and sometimes when stopping. I believe that the scenario is that when you take off, the pinion wants to go up, requiring the driveshaft to shorten slightly, which means that the slip yoke has to push in to the case a little. Since the driveshaft is under a torque load at the time (you are accelerating), the splines in the slip yoke will resist the slip, and when it does finally slip, it clunks. Same thing in reverse when decelerating. To find out if this is your clunk, drop the drive shaft, pull out the slip yoke, and grease the splines. This should make it go away, at least for a while. After about a zillion people complained to GM, there is a TSB on this for some vehicles. They have some special lubricant that they use that is supposed to last longer than regular grease. Otherwise, you can ignore it like I have been doing for about 80,000 miles on my '88 Chevy pickup.

    Tim

    1970 Blazer CST 4X4 350 SM465 NP205
    1987 Suburban 4X4 350
    1988 Chevy Pickup 4X4 350
     
  3. ftn96

    ftn96 1/2 ton status

    Joined:
    Sep 26, 2000
    Posts:
    3,238
    Likes Received:
    0
    Location:
    Nashville Tn
    Thanks. I'll try it. Seems easy and cheap try. If not I probably will ignore until something breaks then the wife will not be able to hound me about upgrades. LOL

    Later
     
  4. Derf00

    Derf00 1/2 ton status

    Joined:
    Jul 25, 2000
    Posts:
    1,683
    Likes Received:
    0
    Location:
    Abilene, TX
    Do you have a Gov-Loc on your rear diff? If you have checked everything you said you have, that might be something to take a look at. If you don't know what all you Jimmy has, take your vin# to your local GMC or Chevy dealer and they can give you all the specs on your Jimmy.
     
  5. ftn96

    ftn96 1/2 ton status

    Joined:
    Sep 26, 2000
    Posts:
    3,238
    Likes Received:
    0
    Location:
    Nashville Tn
    Again, thanks gents.
     
  6. Chris Demartini

    Chris Demartini 1/2 ton status

    Joined:
    Feb 17, 2000
    Posts:
    2,406
    Likes Received:
    1
    Location:
    Dumont NJ 07628
    <font color=blue>Also check the spider gears if you have an open diff. Mine bang and clunk at slow speeds and when coming to a stop.</font color=blue>

    http://www.chrisd71k5.coloradok5.com <font color=blue></font color=blue>
     
  7. EDGE

    EDGE Registered Member

    Joined:
    Aug 12, 2000
    Posts:
    42
    Likes Received:
    0
    Location:
    virginia beach , va
    Thank you for asking that question.I also have that clunk when I put it in drive,come to a stop,or put it in reverse.It sounds like there is no way that it can be making such a horrible sound and not screwing everything up.
     
  8. K5XLR8R

    K5XLR8R 1/2 ton status

    Joined:
    Aug 22, 2000
    Posts:
    210
    Likes Received:
    0
    Location:
    Washington State
    My '86 does this too, it sounds horrible, and makes me cringe everytime!!!
     
  9. Truckfan2

    Truckfan2 1/2 ton status

    Joined:
    Apr 10, 2000
    Posts:
    343
    Likes Received:
    0
    Location:
    Northern IL
    My '89 w/NP241 did that a while ago but it was the u-bolts on the rear axle that had stretched or loosened which cause the axle housing to rotate... I fixed that with new u-bolts. Now I have a 6" lift with a new driveshaft and I think it clunks every now and then... I'll tighten the lift and stuff and see if I still get a clunk.

    Have been stuck (once) as of 8/12/00
    "(2H) Where's all the mud?.(4H)...(4L)..(4H)... oh crap"
     
  10. Blazer1970

    Blazer1970 1/2 ton status

    Joined:
    Feb 17, 2000
    Posts:
    1,600
    Likes Received:
    0
    Location:
    Old Mission, MI
    I will add that what I described above is only one source of a clunk. That one seems to be common to NP241s, and will occur on low mileage trucks without a lot of wear in the drive line. Good point about the U-bolts, they can make that one much worse. With higher mileage, there are a lot of potential clunk sources. Worn 10 bolt rear ends are a good one. The rear end in my Suburban has a lot of wear in the spider gears and cross shaft, and the backlash makes a pretty good clunk when you shift into gear. This one will occur as soon as the tranny shifts, especially from F to R or R to F, even while you still have your foot on the brake. This is different from the clunk that you get on acceleration or deceleration. Backlash is easy to find by getting under the truck and turning stuff by hand. Four wheel drive vehicles have a lot more potential sources of backlash (transfer case, and connection between t-case and tranny) than a car or 2WD truck, so sometimes they just clunk. The trick is to tell the difference between a normal clunk, and something that is about to self-destruct.

    Tim

    1970 Blazer CST 4X4 350 SM465 NP205
    1987 Suburban 4X4 350
    1988 Chevy Pickup 4X4 350
     
  11. Hell my 82 clunks all the time!!LOLI still have the np208,it does the same thing.The only time I worry is when it don't clunk!LOL

    IF IT AINT BIG IT AINT BAD!!!!!!
     
  12. Wheels

    Wheels 1/2 ton status

    Joined:
    Aug 18, 2000
    Posts:
    638
    Likes Received:
    0
    Location:
    Native Floridian living in Oklahoma, USA
    One other area to look at is the slip joint in the drive shaft. My wifes 97 Tahoe had a clunking noise that drove the dealership crazy. The put in a new rear end, tranny, did some spring work, brakes, etc. I pulled the drive shaft and there was no lube in the slip joint. Cleaned it up and put some grease in it and it stopped. Just a thought.
     
  13. ftn96

    ftn96 1/2 ton status

    Joined:
    Sep 26, 2000
    Posts:
    3,238
    Likes Received:
    0
    Location:
    Nashville Tn
    Thanks for all the insights gents. I think I'm going to start at the brakes and work my way forward. Everything back there seems to be cheaper. At least I'll know whats new and whats old when I get done.
     
  14. There is no slip joint in the rear shaft on a 90k5.Just a slip yolk into the tranny.

    IF IT AINT BIG IT AINT BAD!!!!!!
     
  15. ftn96

    ftn96 1/2 ton status

    Joined:
    Sep 26, 2000
    Posts:
    3,238
    Likes Received:
    0
    Location:
    Nashville Tn
    Yes big daddy, you are correct, I have a one piece rear shaft.What all is involved in replacing the slip yolk with a fixed?
     
  16. Wheels

    Wheels 1/2 ton status

    Joined:
    Aug 18, 2000
    Posts:
    638
    Likes Received:
    0
    Location:
    Native Floridian living in Oklahoma, USA
    Should have added slip yoke. That was where the problem was on the Tahoe in the slip yoke. When you gave it the gas, the slight axle wrap would cause the slip yoke to bind then when it became unbound it would give a noticeable clunk. At braking, the reverse wrap would also pull it out slightly and cause it to bind and just after stopping it would release giving a clunk. The clunking sound was from the slip area releasing and becoming unbound. Almost felt like something was loose in the area of the rear end. Like I said, greasing this cured the problem.
     
  17. Blazer1970

    Blazer1970 1/2 ton status

    Joined:
    Feb 17, 2000
    Posts:
    1,600
    Likes Received:
    0
    Location:
    Old Mission, MI
    Didn't I say that in the first response to this post? There is a slip yoke eliminator kit avaiable for the NP241. Someone else will have to help with the source. I think about $300 - $400 for the kit plus a new or modified rear drive shaft - you gotta want it pretty bad.

    Tim

    1970 Blazer CST 4X4 350 SM465 NP205
    1987 Suburban 4X4 350
    1988 Chevy Pickup 4X4 350
     
  18. ftn96

    ftn96 1/2 ton status

    Joined:
    Sep 26, 2000
    Posts:
    3,238
    Likes Received:
    0
    Location:
    Nashville Tn
    Any idea what the name and part number is on this stuff? Called the dealer and they didn't know what I was talking about.

    Will work for beer, parts and tools.
    90-350TBI-TCI700-241-33"-10/12 bolt w/4.10's,
    <A target="_blank" HREF=http://www.nashvillek5.freeservers.com>http://www.nashvillek5.freeservers.com</A>
     
  19. rampage

    rampage 1/2 ton status

    Joined:
    Mar 20, 2001
    Posts:
    2,261
    Likes Received:
    73
    Location:
    Humboldt/Pacifica, CA
    Funny you should ask this question. I had this clunk for years and it seemed to get worse over time (several years). I tried everything to get rid of this including that special slip yoke grease. Finally, about two weeks ago I heard a popping noise (like someone making popcorn but very loud), didn't sound good. I also noticed that the tires started chirping a little while going straight. Definitely not good! I took the rear diff cover off, raised both back wheels and turned one about one revolution and it locked up. My diff was toast. It looked like it had way too much side play in it, about 1/4 inch. I had the rear rebuilt with new gears (4.10) an Eaton limited slip and new bearings. Guess what, that clunk is gone and my rearend is tight once again, just the way my woman likes it *L*. My guess is that you have a gov-lock, just like I did, which I was told seem to have that problem. My suggestion is to be careful when going from park to reverse to drive and it should last you 100k miles (less with heavy wheeling). Good luck.
     
  20. newyorkin

    newyorkin 1 ton status

    Joined:
    May 8, 2001
    Posts:
    16,555
    Likes Received:
    157
    Location:
    Los Estados Unitos
    I had this clunk on my '88 Camaro, and my current '88 K5.
    I get the clunk going park to drive, drive to reverse, etc, etc. Just wear in the driveline somewhere? If I roll backward a little bit before putting the truck in drive, there's no clunk. It's like rolling backward pre-loads the driveline against the clunk going into drive. If I roll back and put it in reverse, the clunk is there.
    Do you have the same symptoms? I never really worried about it, but I wonder now from reading other posts if my rear is about to blow...

    Ratch
    **Hmmm. Land or Mall? Land or Mall? Let's see. Lotsa SUV's around here... Let's build a mall.**
     

Share This Page